Filaments are what solar physicists call Prominences (movie of the day March 25 2018) when they appear on the solar disk. The dark broad feature seen most clearly at 0:02 is such a filament. While much easier to see hanging off the limb of the sun IRIS can observe these features on disk by scanning through the Magnesium II spectral line. Time is this movie represents images of the sun in different wavelengths. Scanning through the different wavelengths allows us to see filaments that are otherwise drowned out by the bright background seen at the beginning and end of the movie.